Planetary or epicyclic gears are known in the art and are generally designed to transfer drive from an input shaft to an output, for example an output shaft or a load connected to the output. In such systems, a number of planet gears are meshed between an outer, or ring gear and a central, or sun gear. The planet gears may be rotationally fixed and able to rotate about their respective axes. If the sun gear is connected to an input shaft, and the ring gear is connected to an output load, then rotation of the input shaft will cause actuation of the output load.
Compound planetary gears are known wherein the input shaft is coupled to multiple output loads. This may be achieved by providing two ring gears and meshing these to the planet gears separately. For example, a first ring gear may be meshed with the planet gears at respective axial ends of the ring gears, and a second ring gear may be meshed with the planet gears at a central axial location.
It is possible to drive the first and second ring gears, and their respective output loads, at different rates by providing different meshing arrangements between the planet gears and the first and second ring gears. For example, the meshing between the planet gears and the first ring gear may have a different amount of teeth than the meshing between the planet gears and the second ring gear.
Most planetary gear systems are used in an environment having restricted space, for example in an aircraft. As such, it is desirable to provide a planetary gear system that is light and compact.